Oftentimes in the process of regenerating ion exchange resins, good practice dictates that, in order to obtain complete regeneration, it is necessary to supply the resin with at least double the amount of regenerant chemical normally required by stoichiometric considerations. As a result, the excess regenerant chemical, mixed with salts which are released by the ion exchange resin during the course of regeneration comprise a waste product which has little or no economic value and which is in fact detrimental due to the fact that disposal problems are commonly encountered.
A typical regenerant used to regenerate ion exchange resins is hydrochloric acid. In many cases, after the hydrochloric acid, at a concentration of about 7%, is flowed over the ion exchange resin to be regenerated and regeneration is completed, a relatively large volume of hydrochloric acid in aqueous solution along with contaminating chloride salts, such as sodium chloride, must be disposed of. The spent or contaminated acid can no longer be used as a regenerant and thus is of little or no economic value. In addition, the spent acid comprises a disposal problem since further treatment of the acid or salts must take place before disposal.
Methods known as acid retardation have been developed whereby an acid-salt mixture is flowed in contact with an anion exchange resin to effect a separation of the acid and salt. However, the prior art methods have not assumed commercial importance due to the fact that only the incomplete separation of the acid and accompanying salt can be obtained. Typical of the prior art acid retardation is an article entitled, "Acid Retardation, A Simple Physical Method for Separation of Strong Acids From Their Salts," reprinted from I and EC, Process Development and Design, by Melvin J. Hatch and John A. Dilland, dated October, 1963. Therein a method of separating sodium chloride and hydrochloric acid is disclosed employing Dow Chemical Company Retardation, a strong base anion exchange resin. The prior art discloses that the resin preferentially retards the travel of an acid fraction down a column with respect to a more rapidly moving salt fraction, thereby enabling a separation of the acid and the salt to be effected.
It is clear, however, that the prior art method of acid separation from metal salts needs to be improved upon to make it economically feasible for use. Accordingly, what is needed is a new method for separating acids from their salts in aqueous solution employing a strong base anion exchange resin in the common anion form.